Layered double hydroxides for H2 generation by the photoreforming of organic compounds

Layered Double-Hydroxides (LDH) materials are promising catalysts for solar-driven reactions thanks to their two-dimensional and the tunability of their composition. The preparation of three bimetallic NiFe-, NiCo- and ZnAl-LDH for H₂ production by the photoreforming of glycerol under UV and visible irradiation has been investigated. Different modifications were studied: calcination, thermal reduction, plus Pt loading and TiO₂ doping. Samples exhibited typical features of LDHs in XRD and hexagonal crystallites and the presence of some satellite bands were observed by HAADF-STEM and XPS, respectively, though only thermal treatments modified partially or completely the LDH structure. NiCo- and ZnAl-LDH have the weakest and the most stable LDH structures, respectively. Finally, on the unmodified NiFe- and NiCo-, and ZnAl-LDH materials, photoactivity showed zero activity toward H₂ production, most likely due to their narrow and wide band gap (BG), respectively, but further thermal modifications, plus the incorporation of co-catalysts such as Pt and TiO₂, promoted photocatalytic activity. On the LDH containing TiO_2, the modifications had variable effect, for instance, Pt photodeposition significantly enhanced activity on ZnAl-LDH, but not on NiFe-LDH.